Las Vegas, NV (My Sportsbook) - Manny Pacquiao added another chapter to a burgeoning legend on Saturday night at the MGM Grand, stopping Miguel Cotto in the 12th and final round of their WBO welterweight championship fight.

The end came at 55 seconds of the 12th, when referee Kenny Bayless stepped in after Pacquiao landed a combination along the ropes to the head of an already battered Cotto.

It was the 50th win in 55 fights of a 14-year pro career for the 30-year-old Pacquiao, who held previous world titles at 112, 122, 130 and 135 pounds, and walked into the ring as the reigning IBO champion at 140 pounds.

Cotto, also a former champion at 140 and a two-time belt-holder at 147, is 34-2.

The loss was his second by TKO in four fights, following an 11th-round defeat to Antonio Margarito in 2008.

"We were very careful in the early rounds because we know what could happen. We were trying to taste his power in the early rounds," Pacquiao said. "We were looking for a KO shot, that's why I didn't throw lot of punches early. I was timing him."

Cotto won the first round by being busier and appeared on his way to winning the second before he was dropped with a quick right hand late in the session. The momentum seemed to turn from that point, with the much quicker Pacquiao (50-3-2, 38 KOs) dominating exchanges with speed and timing.

He dropped Cotto again in the fourth with a left hand and seemed on the verge of a TKO several times in the last few rounds, before Bayless finally ended matters in the 12th.

"That's what I had heard, he's bigger than me and stronger than me, so we tried to accelerate the fight and look for one punch, keep pressuring him and looking for a counter," Pacquiao said. "We tried our best to knock him out."

.com had Pacquiao ahead, 108-99, at the time of the stoppage.

"I didn't see from where the punches were coming and I didn't protect myself from the punches," Cotto said. "I've fought everybody, and Manny is one of the best of all time."

On the undercard, unbeaten Mexican Julio Cesar Chavez Jr. maintained his loss- free record but did little to step up in terms of recognition, winning a unanimous decision over anonymous middleweight Troy Rowland in a 10-round bout in the final bout before the main event.

Chavez, 23, improved to 41-0-1 and swept the scorecards by counts of 99-91, 98-92 and 97-93.

.com had it 98-92 for Chavez.

The win was Chavez's 18th straight since a six-round draw against Carlos Molina in 2005. He weighed in at a career-high 160 pounds in his first bout as a full-fledged middleweight.

His previous top weight had been 156 pounds for a pair of bouts in 2008.

Rowland, a 34-year-old from Grand Rapids, Mich., dropped to 25-3. He had won four straight since a seventh-round TKO loss to Fernando Zuniga in 2005.

Rowland landed 249 punches compared to 238 for Chavez, according to ringside punch statistics.

Belarus-born New Yorker Yuri Foreman became a world champion in his first try on the title-fight level, downing veteran Daniel Santos by unanimous decision to win the WBA junior middleweight crown.

Now 28-0, Foreman took the verdict by scores of 116-110, 117-109 and 117-109.

.com also scored it for Foreman, 116-110.

Santos, a former WBO belt-holder at 147 and 154 pounds, was defending his WBA title for the first time since winning it from Joachim Alcine by sixth-round KO in July 2008.

He is 32-4-1.

Foreman scored knockdowns in the second and 12th rounds and controlled most of the action with superior speed and footwork over Santos, who struggled to make 154 pounds and unofficially put on 19 pounds between the weigh-in and the opening bell.

According to ringside punch statistics, Foreman out-landed Santos, 146-105.

Contender alumnus Alfonso Gomez won his third straight fight since a welterweight title loss to Cotto in April 2008, winning a technical decision over Jesus Soto Karass after the bout was stopped in round six due to a bloody cut caused by an accidental head butt.

Gomez, now 21-4-2, swept the aborted scorecards by counts of 58-54, 57-55 and 57-55.

.com also had it 57-55 for Gomez.

A TKO winner over the late Arturo Gatti in Gatti's last fight in 2007, Gomez sustained an inch-long gash midway through round three against Soto Karass and saw his foe penalized twice for low blows in rounds three and four.

The ringside doctor called a halt to the action at 2:41 of the sixth.

Soto Karass fell to 24-4-3.